Tag Archives: corals

Impacts of climate change on marine communities, seagrass dieback, and a trip to the Abrolhos Islands!

You may have noticed a lack of posts over the last few weeks.  No holiday for me though, here’s a quick taste of some of the other stuff I’ve been up to!

Impact of climate change on marine coastal ecosystems – A masterclass with Nuria Marbá
I was lucky enough to be invited along to present some research at a masterclass at the Institute of Advanced Studies led by Nuria Marbá in late March.  Nuria is a highly respected marine ecologist, and is mainly focussing on researching how coastal communities will respond to climate related stressors such as increased sea surface temperature.  Nuria gave a fantastic talk on the responses of a variety of different coastal ecosystems to projected future warming; from seagrass meadows in the Mediterranean to seaweed communities off the coast of Greenland.   In particular, the seagrass Posidonia oceanica – the real foundation species of the Mediterranean Sea – is at real risk from a combination of increased temperatures and future human activity.  P. oceanica has historically been able to resist disturbance events through extremely long life spans – a study led by Sophie Arnaud-Hound in 2012 suggest that some clones are thousands of years old!!!  However, this long life span is coupled with extremely slow recovery, and it is the really fast rate of expected change in temperature that is expected to cause the P. oceanica meadows to really struggle.  Above average temperatures in the Mediterranean in the last decade has already resulted in significant shoot mortality (Marba and Duarte 2010 Global Change Biology), and the predictions for seagrass response to future warming events look even scarier – with the present consensus being a “functional extinction of P. oceanica meadows by the middle of the century (2049±10), even under relatively mild greenhouse-emissions scenario” (Jorda et al. 2012 Nature Climate Change).  This is all pretty sobering stuff considering that P. oceanica forms the basis of key ecosystems in the Mediterranean Sea.

Closer to home, I presented some initial research that was conducted looking at the effect of the 2011 Marine Heatwave on seagrass populations in Shark Bay.  We travelled up to Shark Bay in March 2011 (right in the middle of the heatwave) as part of a separate research project, and noticed two striking features – water temperatures were far higher than normal, and the dominant seagrass Amphibolis antarctica (wire weed) had experienced severe defoliation (leaf loss) in certain parts of Shark Bay.  Closer analysis showed that the areas worst affected were adjacent to the recently flooded Wooramel River, so we hypothesis that a combination of elevated temperatures and decreased light availability may be leading to the loss of leaves.  Effectively, we believe that the increased temperature increases respiratory demand (the seagrasses get ‘hungrier’ for light) whilst the decreased light availability stops that demand being met.  We are re-visiting previous study sites where defoliation was noticed in an attempt to measure the recovery of the seagrasses; so I’ll keep you posted!

Defoliation in Shark Bay seagrass meadows

A healthy Amphibolis antarctica meadow (left) and a defoliated meadow in Shark Bay (right). We believe a combination of low light availability and elevated tempertaures has led to this loss of leaf material.

Other workshop presentations included a discussion on the impacts of the same marine heatwave on marine communities (in particular, macro algae) up and down the West Australian coastline by Thomas Wernberg, carbon sequestration impliactions from Oscar Serrano-Gras, and a discussion of the effects of warming on feedback in algal assemblages from Scott Bennett.  All in all, a fantastic workshop that will hopefully have positive benefits for the management of marine communities in the face of continued warming of our oceans.

A trip to the Houtmans Abrolhos!
For one week at the start of April I was lucky enough to help out Luke Thomas with his research into coral resilience at the beautiful Houtman Abrolhos.  The Houtman Abrolhos is a chain of small islands located 80km off the coast of Geraldton, Western Australia.  They are really special as they are the highest latitude true coral reef in the Southern Hemisphere.  As such, they may represent an important site that could potentially act as a refuge or a stepping stone for some coral species to move south as temperatures increase.

Acropora research at the Abrolhos Islands

Luke taking samples to investigate coral resilience at the Houtman Abrolhos.

Luke is trying to figure out the genetic connectivity of the corals in the Houtman Abrolhos with those in other locations along the West Australian coast, such as those found in Shark Bay, Ningaloo Reef, and Cygnet Bay.  This will help to determine the resilience of the coral reef communities in the Houtman Abrolhos to future changes in climate (Luke explains things much better than I do here!).  We also carried out some ecological experiments on kelp beds at the same time, so it was a full week of research!  But luckily the weather held up for us and we had some stunning dives – hopefully I’ll be able to post some more photos at a later date!

Kelp research at the Abrolhos Islands

Some fantastic visibility led to some incredible kelp dives (20m depth at this site!) Photo: Gary Kendrick

The inaugural Oceans Institute Student Conference
March also seen a landmark for the UWA Oceans Institute – the first student conference was held at the University Club at UWA.  There were a huge range of talks that showed the breadth of research at the university – everything from tracking marine plastics to studying the biology of pteropods!  And even me trying to get everyone excited about phosphorus cycling in seagrass sediments (what’s more, I was awarded joint first place for the presentation, and won a return trip to Rottnest Island – fantastic!).  One of the highlights from the conference was a talk by renowned marine ecologist Callum Roberts about the pressures facing coral reef ecosystems over the next 100 years.  He was quick to emphasise that warming temperatures aren’t the only threat, with human impacts such as overfishing and pollution likely to lead to worsen negative impacts on these reefs.  Sobering stuff.  On a brighter note, the day as a whole went well, and I think that the 2013 OI student conference will set the benchmark for many more successful conferences in years to come!  Big thanks to Liza, Eric, Renee and the rest of the organising committee!

‘Worldwide diebacks of seagrass ecosystems’: A seminar from Ole PedersenI also had the pleasure of heading along to a seminar from Ole Pedersen; a 2013 Professor-at-Large at UWA.  Ole is one of the authorities in the ecophysiology of aquatic plants (including seagrasses!) and is primarily based at the University of Copenhagen, but is over for a two week stint to do some work in Western Australia!  Ole’s seminar focussed on two potential causes of dieback of seagrass – hypoxia (lack of oxygen) and sulphide intrusion (effectively poisoning!).  Ole has played a leading role in the creation of microsensors that can be used to measure oxygen and sulphide concentrations in the field, and his research indicates the both hypoxia and sulphide intrusion could lead to further loss of seagrass communities as ocean temperatures rise!  I’m lucky enough to be helping Ole and Jens Borum (also visiting from the University of Copenhagen) out with some of their experiments into the potential responses of West Australian seagrass species to changing concentrations of carbon dioxide in the water column, so I should be able to also keep you posted on that research!

As you can see, a busy few weeks, which is why the blog has taken a bit of a back seat!  Rest assured I hope to blog more over the next few weeks!

Marbá, N., & Duarte, C. (2009). Mediterranean warming triggers seagrass (Posidonia oceanica) shoot mortality Global Change Biology, 16 (8), 2366-2375 DOI: 10.1111/j.1365-2486.2009.02130.x

Jordà, G., Marbà, N., & Duarte, C. (2012). Mediterranean seagrass vulnerable to regional climate warming Nature Climate Change, 2 (11), 821-824 DOI: 10.1038/nclimate1533